Multichannel remote transducer monitoring system

ABSTRACT

A transducer monitoring system includes a transducer assembly positioned at a remote location which operates to measure one or more separate physical phenomena. The transducer assembly is coupled to a central location, such as at the top of an oil drilling platform, by means of a single conductor cable. The transducer assembly comprises only passive components, including a stepper switch for separately selecting each of said transducer elements and for enabling current applied to said cable and transducer assembly to generate an output voltage representative of the present state of the resistance of each such transducer element. The improved invention requires only a single constant current pulse periodically applied to the cable to both generate said output voltage and to switch the stepper switch to the next contact. A calibration circuit that measures temperature effects on the transducer assembly and cable is also included.

This is a Continuation-in-Part of application Ser. No. 100,938, filed onDec. 6, 1979 now U.S. Pat. No. 4,322,728.

The present invention is directed to remote transducer monitoringsystems, such as well logging systems, and more particularly to suchsystems wherein one or more physical phenomena may be measured bytransducer elements through the operation of a passive circuit operativeat very high temperatures. The circuit includes a stepper switch and atemperature calibration circuit. This switch is caused to step tosuccessive switch contacts by means of a periodic constant currentpulse. This current pulse also is coupled to a respective transducerelement as a function of stepper switch position. All switching signals,transducer signals and circuit power is transmitted between the remotesystem and a central station by means of a single conductor cable.

Prior art remote transducer monitoring systems have generally beencomplex and unreliable devices. Such devices have either required thatmultiple conductor cable be used or that active devices or other complexcircuitry be included at the remote station. Most are also pulse codedsystems requiring synchronization signals. Such systems have sufferedfrom malfunctions resulting from crosstalk, noise and pulse overshootproblems. U.S. Pat. No. 2,819,408 to Swift, for example, shows asubsurface instrument for well logging connected to the drillingplatform via a single conductor cable, but having a plurality of powersupplies, including batteries, an oscillator and other active elementsat the remote location. In addition, this device measures only a singlecondition, and two different current pulses are required for properoperation thereof. U.S. Pat. No. 3,562,729 to Hurd is another example ofa remote system having a complex circuit including active devices. U.S.Pat. No. 2,564,198 to Elkins illustrates a less complex transducerassembly for well testing, but it includes separate cable conductors forpower to the stepper switch motor and for signals from the transducerelements. Russian Pat. No. 136,832 to Arbuzov illustrates anothermulticonductor remote transducer assembly including a stepper switch.U.S. Pat. No. 2,414,862 to Fearon shows a well surveying apparatus wherea remote stepping motor is actuated by alternating current over a singleconductor cable.

The problem with such prior art devices is that well logging systems orthe like are being required to operate in deep oil or geothermal wellsof much higher down-hole temperatures than in the past, and at greaterdistances from the surface, e.g. of the order of miles from the surface.Prior art devices having active components are generally inoperativeabove about 200° C. Active devices are generally defined as devices thatcan provide power gain greater than unity, e.g., transistor devices.Passive devices, however, are generally devices that cannot act as asource of power, e.g. resistors, capacitors, inductors and relays. Thus,simple, high reliability transducer measuring assemblies operative bymeans of a less expensive single conductor cable, and operative at muchhigher than previously seen temperatures, are desired. The presentinvention provides such high temperature operation advantages since itcomprises only passive components. With the present invention, operationat temperatures several orders of magnitude higher than 200° C. arerealizable. Such single conductor cables are also able to operate inhigher temperature environments, do not have the problem of cross talkwith adjacent conductors, and are more easily handled thanmulticonductor cable.

Accordingly, an object of the present invention is to provide a remotetransducer monitoring system requiring only a single conductor cable.

A further object of the present invention is to provide a transducermonitoring system of simple design and installation, using passivecomponents operative at temperatures above those in which active devicesnormally are able to operate, thereby providing highly reliableoperation in severe remote environments.

Another object of the present invention is to provide a transducermonitoring system wherein both switching and measuring operations of thesystem are enabled by means of a plurality of constant current pulses ofequal magnitude and duration.

A still further object of the present invention is to provide forautomatic temperature calibration means in the transducer assembly atthe remote end of the cable.

These and other objects and advantages of the present invention willbecome more apparent upon reference to the following description and theaccompanying drawing, in which FIG. 1 is a schematic diagram of a remotetransducer monitoring system according to the present invention.

Generally, the present invention is directed to an apparatus formonitoring one or more transducer elements positioned in a transducerassembly at a remote location. More specifically, the present inventionis designed to sense the present pressure and temperature at the bottomof oil or geothermal wells or at other remote stations, as well assensing other physical phenomena, as desired. The apparatus makessuccessive transducer measurements at the remote location over a singleconductor cable by operating a stepper switch. This switch makes contactsuccessively with each transducer element. Conventional transducerelements include variable resistor components. Such resistors vary as afunction of the change in the given physical phenomena to be measured,e.g., the well temperature may cause the resistance to vary at a rate of10 ohms per 100° C.

The stepper switch includes a relay coil which is connected in seriesbetween the single conductor cable and the transducer elements, and isenergized by the constant current pulse sent down said cable from thesurface. Interruption of the energizing current causes the relay coil tostep the switch to the next transducer measuring resistor. While thecurrent is on, it provides means for generating an output voltage acrossthe resistor presently connected thereto via said switch.

The stepper switch operates in a first position to connect the currentpulse to a comparator resistor. At a second position, a calibrationresistor is placed in parallel with the comparator resistor. Insuccessive positions of the stepping switch, one or more respectivesuccessive transducer element measuring resistors are substituted forthe calibration resistor in parallel with said comparator resistor.

As seen in FIG. 1, the main elements of the present invention include atransducer assembly means 10 installable in a simple manner in a deepwell or other remote station. This transducer assembly means 10 isconnected to a central location at the surface of the drilling platform,or at whatever given central location is provided, by means of a singleconductor cable 12. At the surface, the single conductor cable 12 isconnected to a constant current supply 14 and a conventional digitalvoltage meter (DVM), shown at 16. The current supply 14 provides aperiodic current pulse of predetermined fixed amplitude to provideremote transducer assembly operation as hereinafter described. The DVMprovides means for measuring the voltage resulting from the currentoutput by said current supply 14. The single conductor cable may be aone wire line using the earth as a ground return, or it may be astandard single conductor cable with ground return by means of aconventional cable sheath or shield for the cable 12, as showndiagramatically at 18.

The transducer assembly means 10 includes a stepper switch 20 includinga relay coil 22, a swinger arm 24, and a plurality of switch contacts1-6. The stepper switch operates to move the swinger arm 24 to asuccessive switch contact whenever current is terminated from the relaycoil 22. This is enabled since coil 22 is connected in series betweencable means 12 and the swinger arm 24. That is, one pole of said coil isconnected to cable means 12 and its other pole to swinger arm 24.

The swinger arm 24 automatically contacts each successive switch contact1-6 and then on the next current termination returns to switchcontact 1. That is, stepper switch 20 continues to successively contacteach of its switch contacts as a function of the current across relaycoil 22.

The transducer assembly means 10 also includes a plurality of transducerelements indicated at 26, 28, 30 and 32. Each transducer element isdesigned to measure a selected physical phenomena, as described above,such as with a resistively variable temperature probe, or with apotentiometric pressure transducer element. Thus, each transducerelement 26-32 indicates a change in its respective physical phenomenabeing measured by varying its resistance in a conventional manner. Ascan be seen in FIG. 1, each transducer element 26-32 is connectedbetween a respective switch contact of stepper switch 20 and assemblyground, indicated at 38. Thus, successive current pulses from thecurrent supply 14 are coupled across each of the variable resistors ofthe transducer elements 26-32, for generation of an output voltagemeasurable by DVM 16.

To provide an accurate indication of the variation in each of thetransducer resistors 26-32, both a comparator resistor 34 and acalibrate resistor 36 are also included as part of the transducerassembly means 10. The comparator resistor 34 is connected such that itis in shunt with each of the respective transducer element resistors asthey are accessed by the stepper switch 20.

To provide a preliminary indication of the voltage contributiongenerated by the comparator resistor 34, a switch contact position ofthe stepper switch 20, indicated as switch contact 1 in FIG. 1, is leftunconnected, so that the current from the current supply 14 is allowedonly to go through the single path provided by the resistor 34. Notealso that coil 22 is connected in series with resistor 34 and the restof the resistor network, which comprises respectively resistors 26, 28,30, 32 and 36, depending on the position of the stepper switch 20. Theresistance of coil 22 is typically about 50 ohms. Thus, this initialstep of measuring the voltage generated only by the resistor 34 circuitpath also provides means for measuring and thereby taking into accountthe voltage generated across the coil 22.

For best operation of the transducer assembly means 10, both comparatorresistor 34 and calibrate resistor 36 should be resistors of highaccuracy and temperature stability, e.g., a one percent 100 ohmresistor.

The calibrate resistor 36 is connected in parallel with resistor 34 whenthe stepper switch is positioned to contact switch contact 2. This stepenables a user to know precisely what voltage an accurate fixedresistance will generate when connected in parallel with resistor 34.The DVM 16 may be of a type to store this voltage level andalgebraically compare it with the subsequent voltage levels as generatedby the transducer element resistors 26-32.

Thus, in operation, assuming for explanatory purposes that the swingerarm 24 is initially at switch contact 1, a constant current of 100milliamps, for example, is applied to energize relay coil 22 andestablish a maximum output voltage level to the DVM 16. When theconstant current pulse is removed, the relay coil 22 causes the stepperswitch to move the swinger arm 24 to switch contact 2. Then, when theconstant current pulse is reapplied by the current supply 14, an outputvoltage indicative of resistor 34 in parallel with the calibrationresistor 36 is established. Thereafter, when the subsequent currentpulses from current supply 14 cause respective resistors in transducerelements 26-32 to be sequentially switched in parallel with resistor 34,each establishes its own voltage level. These levels are compared withthe voltage level generated by the resistor network comprising resistors34 and 36. Since these latter resistors are stable known resistances,the resistance of each of the transducer elements 26-32 can becalculated from the difference voltages.

It is to be understood that the foregoing description merely illustratesa preferred embodiment of the present invention, and that variousmodifications, alternatives and equivalents thereof will become apparentto those skilled in the art. Accordingly, the scope of the presentinvention should be defined by the appended claims and equivalentsthereof.

What is claimed is:
 1. An apparatus for monitoring physical phenomena ata remote location comprising:a single conductor cable means having anear and a remote end; means for periodically impressing a current pulseof fixed magnitude on said cable means at its near end thereof; atransducer assembly means connected to the remote end of said cablemeans and including one or more transducer elements, each elementvarying in resistance as a function of the change in the physicalphenomena being monitored by said element, and temperature insensitivepassive means for selectively accessing each said transducer element,whereby said transducer assembly means is capable of operation attemperatures substantially in excess of 200° C., comprising:(i) astepper switch having a plurality of contacts and a swinger arm moveablealong said contacts in a predetermined sequence, each said transducerelement coupled to a respective one of said contacts; (ii) means forcoupling said current pulse from said cable means to said swinger arm;(iii) means responsive to the termination of each said current pulse formoving the swinger arm of said stepper switch to the next contact insaid sequence; and means at the near end of said cable means formeasuring the voltage generated by said current pulse.
 2. The apparatusof claim 1 wherein said stepper switch includes a relay coil and whereinsaid means responsive to each current pulse termination comprises theconnection in series of said coil between said cable means and saidswinger arm.
 3. The apparatus of claim 1 wherein said transducerassembly means further comprises a fixed calibrate resistor elementcoupled to one of said contacts on said stepper switch.
 4. An apparatusfor monitoring a plurality of physical parameters at a remote locationcomprising:a single conductor cable means having a near end and a remoteend; means for periodically impressing a current pulse of fixedmagnitude on said cable means at its near end thereof; a transducerassembly means including at least two transducer elements, each elementvarying in resistance as a function of the variation in the parameterbeing monitored by said element, and passive means for selectivelyaccessing each said transducer element comprising:(i) a stepper switchhaving a plurality of contacts, a swinger arm moveable along saidcontacts in a predetermined repeatable sequence, and a relay coil, eachsaid transducer element coupled to a respective one of said contacts;(ii) means for coupling said current pulse from said cable means to saidswinger arm, and including means responsive to the termination of eachsaid current pulse for moving the swinger arm of said stepper switch tothe next contact in said sequence, said means including coupling onepole of said relay coil to the remote end of said cable means and theother pole of said relay coil to said swinger arm; and means at the nearend of said cable means for measuring the voltage generated by saidcurrent pulse.
 5. The apparatus of claim 4 further comprising a fixedcomparator resistor coupled to said swinger arm and a fixed calibrateresistor coupled to one of said contacts on said stepper switch.
 6. Amethod for measuring a plurality of physical parameters by means of atransducer assembly positioned at a remote location and connected to anear location via a single conductor cable means having a near end and aremote end, said assembly including a plurality of transducer elementsand passive means for selectively accessing each said transducerelement, said passive means including a stepper switch wherein each saidtransducer element is coupled to a respective switch contact on saidswitch, comprising the steps of:(a) applying a constant current pulse tosaid cable means at its near end thereof; (b) measuring at said near endof said cable means the voltage generated by said current pulse; (c)switching said stepper switch to a next switch contact in response tothe termination of said current pulse; and (d) repeating of steps(a)-(c).
 7. A method for measuring at least one physical parameter bymeans of a transducer assembly positioned at a remote location andconnected to a near location via a single conductor cable means at itsnear end, said transducer assembly connected to the remote end of saidcable means, said assembly including one or more transducer elements andtemperature insensitive passive means for selectively accessing eachsaid transducer element, whereby said transducer assembly is capable ofcontinuous operation at temperatures substantially in excess of 200° C.,said passive means including a stepper switch wherein each saidtransducer element is coupled to a respective switch contact on saidswitch, and including a calibrate resistor coupled to a first saidswitch contact, comprising the steps of:(a) switching said stepperswitch to said first switch contact in response to the termination of acurrent pulse on said cable means; (b) coupling a constant current pulseonto said cable means at its near end thereof and measuring the voltagegenerated on said cable means thereby; (c) switching said stepper switchto a predetermined next switch contact having a transducer elementconnected thereto in response to the termination of the current pulse onsaid cable means generated in the previous step; (d) coupling a constantcurrent pulse onto said cable means at its near end thereof andmeasuring the respective voltage generated on said cable means by suchelement thereby; (e) repeating of steps (c) and (d) for each transducerelement connected to said stepper switch; and (f) repeating of steps(a)-(e).
 8. The apparatus of claim 4 wherein said passive meanscomprises temperature insensitive means whereby the transducer assemblymeans is capable of continuous operation at temperatures substantiallyin excess of 200° C.
 9. The method of claim 6 wherein said passive meanscomprises temperature insensitive means whereby the transducer assemblyis capable of continuous operation at temperatures substantially inexcess of 200° C.